A widespread technique for inhibiting operation, in certain areas, of wireless user equipment, such as mobile phones or Bluetooth/Wifi transceivers, is to prevent the user equipment to communicate with the mobile telecommunications network.
Occasionally, inhibition may be required for security reasons, but it may also be used for criminal deactivation of systems that rely on wireless communication for signalling an alarm condition, such as security wireless devices of vehicles for transporting valuables.
In order to prevent any communications, devices called jammers are used, which irradiate high power noise signals over at least one communication channel normally used for wireless transmission of information from the user equipment to the mobile network and vice versa. Typically, jammers transmit in the whole band assigned to the system and, in particular, in the downlink band.
The jamming noise signals drown out the signals transmitted by the base station to the user equipment, so that the user equipment cannot discriminate between the base station signal and the noise. Therefore, the user equipment cannot complete any communication session with the mobile network and cannot even signal its jammed condition to the network or to a security agency.